Async Functions in TypeScript

async function fetchUser(id: string): Promise<User> {
  const response = await fetch(`/api/users/${id}`);
  return response.json();
}

// Arrow async function
const fetchUsers = async (): Promise<User[]> => {
  const response = await fetch("/api/users");
  return response.json();
};

// Promise type parameters
type PromiseResult<T> = T extends Promise<infer U> ? U : T;

type Result = PromiseResult<Promise<string>>; // string
type Direct = PromiseResult<number>;          // number

// Promise all with typed results
const [user, posts] = await Promise.all([
  fetchUser("1"),
  fetchPosts("1"),
] as const);
// user: User, posts: Post[]

// Try-catch with unknown error
async function safeFetch<T>(url: string): Promise<T | null> {
  try {
    const response = await fetch(url);
    if (!response.ok) throw new Error(`HTTP ${response.status}`);
    return response.json();
  } catch (error) {
    if (error instanceof Error) {
      console.error(error.message);
    }
    return null;
  }
}